Me again.
This should explain the differences in audio circuits. To adjust the signal level, you need to change the parts highlighted. If it is built with the values shown in the schematics from Amigawiki, it will be too loud and distort.
I checked my rev 2B A600 and it has the values I highlighted as need changing in red. The schematics I have, issued by Commodore, match my A600. It was on this A600 that I obtained the measurements shown previously.